The present invention relates to fiber optic spools and methods of making the same.
Fiber optic spools, like most spools in general, are formed of two flange members positioned on opposite ends of a spool barrel. To prepare a fiber optic spool such that it is capable of receiving an optical fiber, it is common practice to use foam as a winding surface on the barrel of the spool. The foam on the barrel acts as an expansion joint and absorbs dimensional changes that result during thermal cycling of the wound spool since the coated fiber and the spool have significantly different coefficients of thermal expansion. Therefore, the foam should be able to endure thermal extremes without disturbing the integrity of the package.
The spools are formed by joining together two or three components. According to one approach a pair of similar spool members, each including a barrel portion (i.e., a half-length barrel) and an integral flange, are joined together using an adhesive or solvent which welds together the abutting ends of the barrel portions thereof. According to a second approach, a spacer element is joined between the barrel portions of the spool members in a similar manner, thereby affording a spool possessing a longer barrel.
The foam frequently used for fiber optic spools is a closed cell polyethylene available from Sekisui America Corp., Voltek Division (Lawrence, Mass.). This closed cell polyethylene is characterized by a density of 2.40 lbs/ft3 (3.84xc3x9710xe2x88x922 kg/l), a tensile modulus of 505 lbs/in2 (35.5 kg/cm2) (machine direction), and a thermal stability of 4% shrinkage (machine direction) or 3.2% shrinkage (cross-machine direction).
Two basic techniques have been used, in the past, to apply the closed cell polyethylene to the barrel of the spool. In a first approach, a linear piece of foam is cut to size and then wrapped around a mandrel. The ends of the foam are then heat welded such that the foam forms a tube which is open at both ends. The foam tube can be installed on the spool by slipping the tube over the barrel portion of one spool member before the barrel portions thereof are joined together to form the spool. In a second approach, the linear piece of foam (which has been cut to size) is wrapped about the spool barrel and double-sided tape is applied either to the foam or the barrel to secure the ends of the foam to the barrel.
Although the previously used closed cell polyethylene has proven useful, several problems exist with this foam material. First, the closed cell polyethylene is not sufficiently resistant to surface damage (i.e., abrasions) and does not endure the abuse of handling or cabling operations very well. Second, during spooling operations, for instance, centrifugal forces cause the foam to xe2x80x9cgrowxe2x80x9d away from the spool barrel, lifting the foam off of the barrel surface and creating an uneven winding surface. This is particularly true at winding speeds sufficient to wind about 25 m (or more) of optical fiber per second. Third, closed cell polyethylene has a tendency to shrink during or following exposure to temperatures of about 50xc2x0 C. or higher. Such shrinking can create gaps between the foam and the flanges, which may interfere with subsequent optical fiber pay-off from the spool.
Likewise, the above methods of installing the closed cell polyethylene has resulted in additional problems. For instance, when using double-sided tape, gaps typically appear where the foam ends butt together. While small gaps may not necessarily be problematic, it is best-if at all possible-to avoid any exposed gaps.
The present invention is directed to overcoming these deficiencies in the art.
The present invention relates to a fiber optic spool which includes a spool including a barrel having opposed ends, a first flange positioned on one end of the barrel, and a second flange positioned on the other end of the barrel; and an elastic foam tube substantially surrounding the barrel under conditions whereby the foam tube is stressed radially while in its resting state on the barrel such that the foam tube resists lifting away from the barrel during rotation of the spool at speeds effective to wind or unwind at least about 25 m of optical fiber per second.
Another aspect of the present invention relates to a method of making a fiber optic spool of the present invention. This method includes assembling a spool including a barrel and flanges positioned on opposite ends of the barrel, and installing about the barrel a foam tube which is elastic and, prior to installing, has an inner circumference that is smaller than the outer circumference of the barrel.
The present invention also relates to a fiber optic spool which includes a spool including a barrel having opposed ends, a first flange secured on one end of the barrel, and a second flange secured on the other end of the barrel; and a multi-laminar cushioning device having a first layer including an open cell foam or closed cell foam and a second layer including a protective material which is connected to and substantially covers the first layer, wherein the multi-laminar cushioning device is in the form of a tube which substantially surrounds the barrel of the spool with the first layer resting against the barrel surface.
A related aspect of the present invention is a substantially tubular, multi-laminar cushioning device which includes an inner layer including an open cell foam or closed cell foam and an outer layer including a protective material which is connected to and substantially covers the inner layer. The substantially tubular, multi-laminar cushioning device is preferably sized and configured for installation on the barrel of a fiber optic spool.
Yet another aspect of the present invention relates to a method of making a fiber optic spool which includes assembling a spool including a barrel and flanges position on opposite ends of the barrel, and installing about the barrel a substantially tubular multi-laminar cushioning device of the present invention.
Still another aspect of the present invention relates to a method of winding optical fiber onto a spool. This method includes providing an optical fiber spool including a barrel and flanges positioned on opposite ends of the barrel, and a cushioning device which substantially surrounds the barrel and resists lifting away from the barrel during rotation of the spool at a velocity sufficient to wind 25 m or more of optical fiber per second; and winding optical fiber onto the optical fiber spool.
By combining the new cushioning devices of the present invention with suitable spool assemblies, it is possible to achieve fiber optic spools that overcome some or all of the aforementioned deficiencies in the prior art. Either through the use of adhesives, pre-stressed cushioning devices, or multi-laminar cushioning devices, the spools are able to rotate, at speeds sufficient to take-up or pay-out up to about 40 m or more of optical fiber per second, without resulting in cushioning device xe2x80x9cgrowthxe2x80x9d. Moreover, by selecting desirable materials, it is possible to expand the longevity of the cushioning devices employed in fiber optic spools of the present invention, either by minimizing shrinkage of the materials or by rendering them better able to endure physical abuse.
Additionally the inventive foam has a lower density than that of foams previously used on an optical fiber spool. Also the inventive foam has exhibited a reduced elongation during use than foams previously used on an optical fiber spool. Furthermore, the inventive foam has exhibited a higher tensile modulus than previously exhibited by foams previously used on an optical fiber spool. The invention also reduces elongation of the foam during use by introducing residual tensile stresses in the foam prior to and after use.